This invention relates to bisbenzocyclobutene compounds (bisBCBs) containing hydrophobic substituents. An extensive review of benzocyclobutenes is Kirchhoff and Bruza's monograph "Benzocyclobutenes in Polymer Synthesis" (Prog. Polym. Sci., Vol 18, 85-185, 1993), herein incorporated by reference.
Polymers derived from benzocyclobutenes (BCBs) (of which bisBCBs are a subset) are described in U.S. Pat. No. 4,540,763. These polymers are prepared by subjecting BCBs to temperatures sufficient for polymerization. The polymers exhibit properties that make them useful for preparing composites, coatings, and films.
One useful property is a low dielectric constant. It is possible, as Kirchoff reports (pg 92 of the above-cited monograph), to prepare low dielectric constant hydrophobic benzocyclobutene polymers by starting with precursor monomers that contain hydrocarbon or siloxane groups interspersed between the reactive moieties of the monomer molecule. For example, the polymer of the divinylbenzene bisbenzocyclobutene compound shown below has a dielectric constant of 2.7.
Unfortunately, this compound has a melting point of 150.degree.-152.degree. C. which makes processing prior to polymerization time-consuming and costly. ##STR2##
Schrock addressed this deficiency in the art (U.S. Pat. No. 4,812,588) by preparing the liquid, tetramethyldivinyldisiloxane bisbenzocyclobutene (DVS-bisBCB), which is represented by the following structure: ##STR3##
The polymer formed from DVS-bisBCB, poly-DVS-bisBCB has a low dielectric constant (2.55 at 1 MHz) a low dissipation factor (0.0008 at 1 MHz and &lt;0.002 at 10 GHz), and low water absorption (0.25% at 100.degree. C. for 24 hours). (See Kirchhoff et al., J. Macromol. Sci.-Chem., A28(1&12), pp. 1094 and 1104-1106.) Thus, poly-DVS-bisBCB is especially electrically resistive and hydrophobic.
One disadvantage of DVS-bisBCB is that it is not isolated as a single compound, but rather as a complex mixture of compounds. Since the composition of this mixture may vary from batch to batch, the nature of the polymer derived from the DVS-bisBCB monomer may also vary. Thus, there is a potential problem of variability in the properties of the polymer.
In view of the deficiency in the art, it would be desirable to have bisbenzocyclobutene compounds that were liquids at room temperature. At the same time, it is essential that the same desirable properties of the prior art polymers--low dielectric constants, low dissipation factors, and low water uptake--not be compromised.